Aermod.inp: I got the same values both PM10 and PM2.5

Currentely, I’m using “MODELOPT CONC FLAT ELEV BETA” in the aermod.inp. My sfc and pfl files are generated from WRF (using MMIF). I’d like to model the PM10 and PM2.5 in AERMOD. However, when I did tests (using the same emission rate) I got the same values both PM10 and PM2.5. I think could be due to the “CONC” parameter. While we know the PM2.5/PM10 ratio must be less than 1. I would expect to have slightly different values, but not exactly the same. What would be the right MODELOPT configuration to consider the particle size in the horizontal dispersion.

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